The present invention relates to shock absorbers that generate a damping force by controlling a flow of hydraulic fluid in response to a stroke of a piston rod.
Tube-type shock absorbers attached to suspension systems of vehicles, for example, automobiles, are generally arranged as follows. A piston with a piston rod connected thereto is inserted in a cylinder having a hydraulic oil sealed therein as a hydraulic fluid. A stroke of the piston rod causes sliding movement of the piston in the cylinder, which in turn induces a flow of hydraulic oil. The hydraulic oil flow is coat roiled by a damping force generating mechanism, which comprises an orifice, a disk valve, etc., to generate a damping force. Shock absorbers of this type include one in which a reservoir having a hydraulic oil and a gas sealed therein is connected to the cylinder to compensate for a cubic capacity change in the cylinder caused by the entry and exiting of the piston rod into and from the cylinder and a volumetric change of the hydraulic oil due to a temperature change. More specifically, such a cubic capacity change and a volumetric change are compensated for by the compression and expansion of the gas in the reservoir.
In a shock absorber having a reservoir as stated above, if the gas in the reservoir gets mixed into the hydraulic oil as bubbles or dissolves in the hydraulic oil, aeration or cavitation may occur, causing the damping force to become unstable. Under these circumstances, Japanese Patent Application Laid-Open Publication No. 2012-72857 discloses a shock absorber having a baffle plate disposed in the reservoir. With this structure, an inlet port through which the hydraulic oil flows into the reservoir from the damping force generating mechanism can be isolated from the oil surface in the reservoir, and it is possible to gradually enlarge the flow path area of hydraulic oil flowing into the reservoir from the damping force generating mechanism. Accordingly, it is possible to suppress the gas in the reservoir from getting mixed into the hydraulic oil as bubbles or from dissolving in the hydraulic oil and hence possible to suppress the occurrence of cavitation and aeration.
However, there is a demand that the occurrence of aeration and cavitation be suppressed without providing a baffle plate in the reservoir as in the shock absorber disclosed in Japanese Patent Application Laid-Open Publication No. 2012-72857, thereby increasing productivity.